1. Field of the Invention
The present invention relates to a clamping machine, such as die-cast machines or injection molding machines (hereinafter, referred to as molding machines), and particularly to a clamping machine which effects a drawing-out operation of tie bars on exchanging molds using a driving mechanism of movable die plates.
2. Prior Art
In clamping machines, such as die-cast machines, tie bars may affect both new and used molds when they are exchanged. In particular, in the case of die-cast machines, one or more core cylinders are often attached to a mold in the horizontal direction. In such a case, tie bars should be drawn out from fixed die plates, prior to exchange of molds, such that the tie bars will have no influence on the core cylinder.
In conventional clamping machines, special hydraulic cylinders are provided for drawing out the tie bars. However, the hydraulic cylinder of this type has a relatively long cylinder stroke, and thus tie bars are to be moved behind to a distance. Therefore, a predetermined space accommodating the movement should be provided behind the machine. In the case of large-sized die-cast machines, in addition to a long stroke of the special hydraulic cylinder, heavy tie bars themselves are also responsible for lengthening their moving time. Moreover, since the tie bars should be drawn into fixed fie die plates again after new molds are attached to the device, it should take a considerably long time to carry out the whole cycle for exchanging molds.
In conventional clamping machines, devices which are driven by a toggle link mechanism have been widely used. In the case of die-cast machines provided with such a toggle mechanism, however, a link housing is arranged for adjusting the mold thickness to be carried out after exchanging new and used molds. Thus, the entire length of these machines should be considerably long. Accordingly, while the clamping machines of such a toggle link type have a merit in that both of the make-and-break (opening-and-closing) operation and the clamping operation of the molds can be performed by a toggle link mechanism, another type of devices, which include a driving mechanism for the opening-and-closing operation and another driving mechanism for the clamping operation in place of the toggle link mechanism, have emerged recently.
In this case, a clamping cylinder for the clamping operation is arranged on the side of the fixed die plate or of the movable die plate. Since the clamping cylinder cannot accommodate adjustment of the mold thickness alone, various mechanisms have been proposed for driving the clamping operation related to adjustment of the mold thickness.
However, we have not known so far any clamping devices in which efficiency of the above-described drawing-out operation of tie bars and simplicity of the mechanisms are well considered.
Among clamping devices including a clamping cylinder arranged on the side of the fixed die plate, an example of the prior art, which enables tie bars to be drawn out with ease using a make-and-break operation of the movable die plate will be explained with reference to Japanese Patent No. 1996-5060 (TOKUKOUHEI No. 8-5060).
FIGS. 7 and 8 illustrate a clamping machine disclosed in Japanese Patent No. 1996-5060, respectively. FIG. 7 is a front view of a clamping machine, showing a state in which tie bars are drawn out from a fixed die plate, and FIG. 8 is a view of the clamping machine in FIG. 7, showing a state immediately prior to closing molds.
In FIGS. 7 and 8, 201 is a fixed die plate which is fixed to one end of a base (not shown), and to which a fixed mold 202 is attached. 203 is a movable die plate which is mounted to the base movably in both front and back directions, and to which a movable mold 204 is attached. 205 are tie bars, and one end of each tie bar is fixed to the movable die plate 203 with a nut 207. The other end of each tie bar 205 includes a screw portion 206 which mates or engages with half nuts 208. On the rear side of a mold attachment surface of fixed die plate 201 a half nut attachment plate 210 is attached, and four half nuts 208 are provided corresponding to each tie bar 205 across the attachment plate 210. Each half nut 208 is opened and closed, for example, by an effect of a hydraulic cylinder 209 or the like, and is constructed to mate with the corresponding screw portion 206 of the tie bar. The half nut attachment plate 210 is attached to the fixed die plate 201 so as to enable the horizontal movement of the plate 210 in the same direction as the moving direction of movable die plate 203 using a linear guide 211 at a lower surface of the fixed die plate 201 and a linear guide 212 (a bush or the like) at a side surface thereof.
The linear guide 212 is composed of a guide bar 213 fixed to the half nut attachment plate 210, a bush 214 fixed to the fixed die plate 201, and a compression spring 215 attached between the guide bar 213 and the bush 214. The compression spring applies a force to the half nut attachment plate 210 such that it is always pulled toward the fixed die plate 201.
216 is a mold thickness adjusting device to adjust the tie bar screw 206 and the corresponding screws of half nuts 208 to always take positions for enabling their mating even when the thickness of the mold is changed. A pulse motor 220, to which a screw 218 is connected directly, is attached rotatably to a rack 217, and the rack 217 is connected to a bottom face of the movable die plate 203. 221 is a body holding a nut 219, and a rod 222 projecting toward the fixed dies plate 201 is fixed to the body 221.
230 is a cylinder for opening and closing molds, in which a cylinder body is attached to the fixed die plate 201, while a distal end of the cylinder rod is attached to the movable die plate 203, so that the movable die plate 203 can be moved in both front and back directions. 231 is a cylinder for increasing clamping pressure, which is incorporated in the fixed die plate 201. 232 is a ram which is moved in the right direction in FIG. 6 by applying pressurized oil into an oil chamber 234 when the clamping pressure is increased, and pushes the half nut attachment plate 210 at its distal end 233. In this case, the half nuts 208 mate with the corresponding screw 206 of the die bar, thereby to generate a clamping force. 235 is also an oil chamber.
Next, the operation of this clamping machine is explained.
When pressurized oil is supplied to the oil chamber on the rod side of the mold opening-and-closing cylinder 230, the movable die plate 203 advances toward the fixed die plate 201 to perform a mold closing operation. FIG. 8 illustrates a state immediately prior to closing molds when a distal end of the rod 222 of mold thickness adjusting device 216 contacts with the half nut attachment plate 210. The mold closing operation further continues from this state, and the distal end of the rod 222 pushes the half nut attachment plate 210 so that the attachment plate 210 is moved in the horizontal direction following the guide of linear guides 211, 212. When the fixed mold 202 and the movable mold 204 mate with each other completely, the mold closing operation is completed. Then, the horizontal movement of the half nut attachment plate 210 is stopped.
In FIG. 8, threads of the tie bar screw 206 and those of the half nuts 208 are shown to have substantially the same positions, so that the half nuts 208 cannot be closed because both of the thread portions meet on closing the half nuts in such a state. A distance that the half nut attachment plate 210 moves from a time when the rod 222 contacts with the half nut attachment plate 210 to a time when the mold closing is completed may translate to a distance to be corrected such that the tie bar screw 206 and the screws of half nuts 208 may mate properly with each other, and is determined automatically by a length L1 of molds. For example, a distance L0 from a mold attachment surface of the movable die plate 203 to a start point of cutting the tie bar screw 206 is predetermined, and thus the positions of peaks (or threads) and valleys of the screw can also be known in advance.
Meanwhile, with respect to the positions of peaks and valleys of the half nuts when the molds are closed and when the half nut attachment plate 210 is not moved horizontally, since the thickness L1 of the molds, a length L2 from a mold attachment surface of the fixed die plate 201 to a half nut attachment surface of the half nut attachment plate 210 are predetermined, so that the positions of peaks and valleys of the half nuts 208 can also be known in advance with calculation of the sum of (L1+L2). Accordingly, comparing the positions of threads (peaks) of the screw in the tie bar 205 to the positions of valleys of the half nuts 208, a displacement from a proper mating position can be known. This is a value to be adjusted and determined as a moving amount of the half nut attachment plate 210. Namely, knowing only the mold thickness L1, the corresponding amount of adjustment can be known automatically.
The above-described amount of adjustment, i.e., the displacement amount of the attachment plate 210 is determined by a distance L3 from the mold attachment surface 203 of movable die plate 203 to the distal end of rod 221 of the mold thickness adjusting device 216. In this case, a pulse signal corresponding to the amount of adjustment is transmitted to a pulse motor 220 to rotate a screw 218. Thus, the rod 222 is moved to set a position of the attachment plate 210. Accordingly, in the mold closing operation immediately after attachment of molds, the distance L3 is set at an original point. When a completely mold-closed state is reached, the mold thickness L1 is detected by an automatic reading apparatus (not shown), calculating the amount of adjustment, projecting the rod 222 by driving the pulse motor 220, and moving the half nuts by the calculated distance. In this stage, the projected rod 222 may not be moved again as long as the same molds are used, so that it could effect opening-and-closing operations repeatedly while remaining in a fixed state. After the molds are closed and half nuts 208 are moved by the calculated distance, the half nuts 208 are closed together by an effect of the hydraulic cylinder 209.
Next, when supplying pressurized oil into the oil chamber 234 of oil hydraulic cylinder 231, the ram 232 is moved toward the half nut attachment plate 210 and pushes the plate at its distal end 232. Thus, the attachment plate 210 and the half nuts 208 are urged in the right direction, with the half nuts 208 meshing with the tie bar screw 206. In this way, a force for clamping the molds is generated.
When the molds are opened after the molding operation, the pressure in the oil chamber 234 of hydraulic cylinder 231 is lowered, and the half nuts 208 are opened by the effect of the hydraulic cylinder 209. Thereafter, when supplying pressurized oil on the side of the head of mold opening-and-closing cylinder 230, the movable die plate 203 is urged in the left direction to move the molds. At the same time, the half nut attachment plate 210 is moved toward the fixed die plate 201 by extension of the compression spring 215 and returns to its original position. In this case, besides the extension force of compression spring 215, the restoring force may be augmented positively by supplying pressurized oil into the oil chamber 235 of hydraulic cylinder 231. The tie bar screw 206 and half nuts 208 may be replaced by a plurality of circumferential grooves.
However, in the clamping machine disclosed in Japanese Patent No. 1996-5060, while adjustment of the mold thickness is facilitated as described above, the device has the following four problems.
(1) Since one end of each tie bar 205 is fixed securely to the movable die plate 203, the tie bar 205 should be drawn out from the fixed die plate 201 every time the die plate 203 is moved for a mold opening-and-closing operation during a molding cycle, the energy consumed is considerably large.
(2) The tie bars 205, when the molds are opened, are supported in a cantilever state by the movable die plate 203. Therefore, the tie bars may tend to bend in the operation.
(3) While the half nuts 208 for mating with the screw portion 206 of each tie bar 205 is provided on the side of the fixed die plate 201, the mold thickness adjusting device 216 is located on the side of the movable die plate 203. Displacement by a predetermined distance of a lower portion of the half nut attachment plate 210 using the rod 222 against a bias force of the spring 215 requires a complicated mechanism.
(4) The ram 232, which is a piston of the cylinder 231 for increasing the clamping pressure, presses the half nut attachment plate 210 at its right end on increasing the clamping pressure, and each tie bar 205 is moved in the right direction by the force transmitted thereto through the screw portion 206 mating with the half nuts 208, thus applying a clamping force to the movable die plate 203. However, when opening the molds after a product is molded, application of pressure to the ram 232 is stopped, and it is not involved in the initial mold-opening operation. Namely, including the initial mold-opening operation, the whole cycle for opening the molds is performed by the mold opening-and-closing cylinder 230. Since a considerably large force is required for the initial mold opening operation, a hydraulic cylinder which can generate a large power sufficient for moving the movable die plate 203 should be used as the cylinder 230.
We found that the above-mentioned problems can be solved by providing a construction such that one end portion of each tie bar is always connected with a fixed die plate, except of the operation for drawing out the tie bar on exchanging molds, in a straight-hydraulic mold clamping machine which applies a clamping force to molds using a clamping cylinder comprising annular pistons arranged on the side of the fixed die plate.
Accordingly, it is an object of the present invention to provide a new clamping machine which can perform a straight-hydraulic mold clamping and a tie-bar drawing-out operation in a reduced working space, and enables a shortened mold exchanging time, without using a drawing-out cylinder exclusively used for drawing out tie bars, by effecting retraction of a movable die plate and a tie-bar drawing-out operation simultaneously.
In order to accomplish the above-mentioned object of the present invention, the clamping system according to the present invention is provided mold opening and closing means for driving said movable die plate to advance to and retract from said fixed die plate; tie bars each extending through said movable die plate and said fixed die plate for guiding said movable die plate, and having a first engagement portion in which a groove is formed at a rear end on the side of said movable die plate and a second engagement portion in which a groove is formed at a front end on the side of said fixed die plate; a mold clamping cylinder including annular pistons in which said tie bars are fitted slidably and concentrically, first oil chambers each having a larger pressure receiving surface disposed on one side of each annular piston and generating a clamping force to clamp said fixed mold and movable mold subjected to a mold closing operation by an effect of pressurized oil supplied to the surface, and second oil chambers each having a smaller pressure receiving surface on the other side of each annular piston and generating an initial releasing force on an initial mold opening operation by an effect of pressurized oil supplied to the surface, and being incorporated in said fixed die plate; first connecting means disposed on an opposite side of a mold attachment surface of said fixed die plate, having half nuts for engaging with said first connecting portions on the side of said fixed die plate, for connecting distal ends of said tie bars to said die plate detachably; second connecting means disposed on an opposite side of a mold attachment surface of said movable die plate, having half nuts for engaging with said second connecting portions on the side of said movable die plate, for connecting rear ends of said tie bars to said movable die plate detachably; and force transmitting means for connecting said annular pistons of the mold clamping cylinder and said first connecting means so that these are moved together, and transmitting, in cooperation with said first connecting means, an initial releasing force for pushing said tie bars toward said movable die plate and a mold clamping force for drawing said tie bars toward said fixed die plate, to said tie bars in corresponding directions, respectively.
According to the present invention, since a drawing-out tie-bar operation is effected by a driving means which effects also mold opening-and-closing operations of a movable die plate, there is no need to provide a hydraulic cylinder exclusively used for drawing out tie bars, and the operational cost can be saved due to simplification of the mechanism.
A usual operation is carried out, with tie bars being connected to a fixed die plate, and the drawing-out operation of tie bars is effected only when molds are exchanged. The energy can be saved, and the tie-bar drawing-out operation can be started only by disengaging a distal end of each tie bar from each half nut, which is a first engaging means on the side of the fixed die plate. Thus, the time required for starting a mold exchanging operation can be greatly reduced.
In a drawing-in operation of tie bars after exchanging molds, an axial position of each tie bar can be set only by contacting a distal end of the tie bar with a stopper.